SiC-based materials are employed from a multiplicity of different applications, especially where high stability at high temperature or high corrosion resistances are required. Highly porous, light weight SiC-based ceramics are used to an increasing extent as supports for catalysts and as filter materials for the purification of waste gases at high temperature.
In particular, filters are used for examples in order to reduce the proportion of soot in the exhaust gas of a diesel engine.
Filters can be also coated with catalyst in order both to support the combustion of the soot and the oxidation of residual hydrocarbons and carbon monoxide and selective catalytic reduction (SCR) for NOx reduction.
Filters may take the form of wall-flow monoliths.
Ceramic wall-flow monoliths are the most common type of diesel filter substrate. They are distinguished, among other diesel filter designs, by high surface area per unit volume and by high filtration efficiencies. Monolithic diesel filters consist of many small parallel channels forcing the diesel aerosol through the porous substrate walls that act as a mechanical filter. To reflect this flow pattern, the substrates are referred to as the wall-flow monoliths.
Wall-flow filter walls have a distribution of fine pores that have to be carefully controlled in the manufacturing process. Total material accessible porosity is typically between 45 and 50% or higher. Filtration mechanism on monolith wall-flow filters is a combination of cake and depth filtration. Typically, monolith filters have filtration efficiencies between about 70 and 95% of total particulate matter (TPM).
Wall-flow monoliths are typically made up of porous ceramic materials. Two materials most commonly used in commercial filters include cordierite and silicon carbide (SiC).
Commercial high porosity filters, such as with accessible porosity higher than 55% are in general highly brittle and thus very fragile.
Current production methods for SiC filters are also highly energy consuming as these operate at high temperature and require several steps rendering production cost very high.
Hence, a high porosity silicon carbide filter with enhanced mechanical stability would also be advantageous.
Furthermore, an improved method of producing a high porosity silicon carbide filter which is less energy consuming, reduces the amounts of steps needed and thus reduces its cost would be advantageous.